Anode for cathodic protection



Jan. 22, 1963 w. G. WAITE 3,074,876

ANODE FOR CATHODIC PROTECTION Filed May 15, 1958 United States Patent Ofilice 3,074,876 Patented Jan. 22, 1963 3,074,876 ANODE FOR CATHODIC PROTECTIIQN William Godfrey Waite, London, England, assignor to F. A. Hughes dz Q0. Limited, London, England Filed May 15, 1958, Ser. No. 735,600 Claims priority, application Great Britain May 20, 1957 Claims. (Ci. 204-197) This invention relates to the cathodic protection of ferrous metal structures against corrosion by the provision, in electrical connection therewith, of consumable or sacrificial anodes made of a metal or metal alloy anodic to the metal of the structure. The anodes may desirably be made of magnesium base alloy.

It is recognised that in the protection of ferrous metal structures immersed in seawater it is desirable to provide a high initial current density for a limited time, with the object of polarising the structure and so enabling protection to be maintained subsequently with a lower current density. For this purpose it has been proposed to provide a combination of main anodes with the subsidiary anodes of larger surface-to-volume ratio than the main anodes. While this is generally satisfactory, there are sometimes certain practical difficulties. For instance, if the subsidiary anodes are separate from the main anodes considerably more labour and expense is involved in the fixing and the subsidiary anodes themselves tend to become consumed preferentially at or near the point of connection and the whole of the subsidiary anode itself may not therefore be usefully employed. In addition, anodes of relatively small volume but large surface area are likely to sustain damage in moving water. Alternatively, if subsidiary anodes are provided which radiate from the main anode they cannot as heretofore constructed be conveniently of large enough surface area to provide sufficiently high initial current owing to the difiiculty of handling and mounting without damage.

The object of the present invention is to provide a single anode which will give a high current for initial polarisation of the structure with automatic reduction in output over a period of time to the lower level required for maintenance. For this purpose, we provide an anode having a large central mass surrounding a central core by which it can be mounted, a pair of long tapering fins projecting from the mass radially in opposite directions and a pair of short fins projecting radially from the mass in opposite directions at about right angles to the long fins. Each short fin in radial view is tapered and has two curved surfaces merged into the tapering sides of the long fins, each part of said curved surface being of less distance from the axis of the cen-- tral mass than the radial dimensions of the short fins. By this means in operation proximity or interference effects are reduced at the ends of the long tapering fins so as initially to allow unrestricted output. The long tapering fins are therefore consumed from the ends until they reach the approximate dimensions of the short fins. The proximity or interference effects occasioned by the short fins reduce current output, and consequently consumption of the anode, about the point where the long tapering fins join the main body thus preventing the possibility of selective attack at these points which could otherwise result in the loss of the long fins before they were usefully consumed.

The radial length of the short fins may be between 40% and 60% of the radial length of the long fins and the axial length of the anode may be as required to produce the necessary current output.

The core may be constructed according to the invention described in the specification of United States patent application No. 713,727, now abandoned.

The invention is illustrated by way of example in the accompanying diagrammatic drawings, wherein:

FIGURE 1 is a side elevational view of an anode made in accordance with the invention;

FIGURE 2 is a plan view of FIGURE 1; and

FIGURE 3 is an end elevation looking in the direction of the arrow 3 on FIGURE 2.

The anode has a large central mass 10 surrounding a central core 11, e.g. an iron rod (or tube) by which it can be mounted. The block it} has two pairs of fins 12, 13 and 14, 15 which are integral with the block. The fins 12, 13 are in line and offset 180 from each other around the axis of the core. The fins 14, 15 are in line and offset 180 to each other and offset to the fins 12, 13, so that the fins 12, 13 project radially in opposite directions as also do the fins 14, 15. All the fins are tapered and each tapering side of a short fin merges into the adjacent tapering side of a long fin by a curved surface as shown at 17. The fins 14, 15 have a radial length 18 which is between 40% and 60% of the radial length 19 of the long fins. The surface 17 approaches as at 20 at a distance nearer to the core than the radial distance 18 of the short fins.

The axial length 22 of the anode is from to 280 percent of the radius 18 of the short fins.

I claim:

1. An anode for the cathodic protection of ferrous metal structures comprising a large central mass of the anodic metal surrounding a central core by which it can be mounted, a pair of long tapering fins projecting from the mass radially in opposite directions, and a pair of short fins projecting radially from the mass radially in opposite directions at about right angles to the long fins.

2. An anode as claimed in claim 1 wherein the short fins extend to a radial distance between 40% and 60% of the radial length of the long fins, each short fin in axial view being tapered and having two curved surfaces which merge into the tapering sides of the long fins, each said curved surface having a part of less distance from the axis of the central mass than the radial dimension of the short fins.

3. An anode for the cathodic protection of ferrous metal structures comprising a large central mass of the anodic metal surrounding a central core by which it can be mounted, a pair of long tapering fins projecting from the mass radially in opposite directions, and a pair of short fins projecting radially from the mass radially in opposite directions at about right angles to the long fins, said short fins extending to a radial distance between 40% and 60% of the radial length of the long fins, each short fin in axial view being tapered and having two curved surfaces which merge into the tapering sides of the long fins, each said curved surface having a part of less distance from the axis of the central mass than the radial dimension of the short fins, the axial length of the anode being from 150% to 280% of the radius of the short fins.

References Cited in the file of this patent UNITED STATES PATENTS 1,435,671 Stewart Nov. 14, 1922 FOREIGN PATENTS 347,333 France Jan. 4, 1905 683,629 Great Britain Dec. 3, 1952 

1. AN ANODE FOR THE CATHODIC PROTECTION OF FERROUS METAL STRUCTURES COMPRISING A LARGE CENTRAL MASS OF THE ANODIC METAL SURROUNDING A CENTRAL CORE BY WHICH IT CAN BE MOUNTED, A PAIR OF LONG TAPERING FINS PROJECING FROM THE MASS RADIALLY IN OPPOSITE DIRECTIONS, AND A PAIR OF SHORT FINS PROJECTING RADIALLY FROM THE MASS RADIALLY IN OPPOSITE DIRECTIONS AT ABOUT RIGHT ANGLES TO THE LONG FINS. 